6.  THE  ORIGIN  OF  A  POLYDACTYLOUS  RACE  OF 
GUINEA-PIGS 


BY 

W.  E.  CASTLE 


PAPERS  OF  THE  STATION  FOR  EXPERIMENTAL  EVOLUTION  AT  COLD  SPRING  HARBOR, 
NEW  YORK,  No.  6 

CONTRIBUTIONS  FROM  THE  ZOOLOGICAL  LABORATORY  OF  THE  MUSEUM  OF  COMPARATIVE 
ZOOLOGY  AT  HARVARD  COLLEGE.     E.  L.  MARK,  DIRECTOR.     No.  176 


OH 


6.  THE  ORIGIN  OF  A  POLYDACTYLOUS  RACE  OF  GUINEA-PIGS. 


BY  W.  E.  CASTLE. 

1.    FIRST   APPEARANCE    OF   THE   POLYDACTYL   CHARACTER. 

Normal  guinea-pigs  have  four  toes  on  each  front  foot  but  only  three 
on  each  hind  foot.  The  race  of  guinea-pigs  whose  origin  is  to  be  described 
differs  from  ordinary  guinea-pigs  in  possessing  four  digits  on  each  hind 
foot  instead  of  three.  The  four  digits  of  the  front  foot  apparently  corre- 
spond with  digits  2-5  of  the  typical  five-fingered  appendage,  while  the  three 
digits  of  the  hind  foot  correspond  with  digits  2-4  of  the  typical  appendage. 
In  other  words,  all  guinea-pigs  have  lost  from  the  front  foot  the  digit  which 
corresponds  with  our  thumb,  and  normal  guinea-pigs  have  lost  from  the  hind 
foot  two  digits,  which  correspond  respectively  with  our  "  great "  and 
"  small  "  toes.  In  the  race  to  be  described  the  "  small  toe  "  is  present  on 
the  hind  foot  as  well  as  on  the  front. 

In  October,  1900,  several  ordinary  guinea-pigs  were  obtained  from  a 
nearby  breeder,  one  pair  of  which  produced  in  the  following  June  three 
male  young.  The  largest  of  these  young  bore  an  imperfectly  developed 
digit  on  its  left  hind  foot,  in  the  position  of  a  "  small  toe."  This  toe  bore 
a  well-developed  claw  and  apparently  contained  the  bony  phalanges,  but 
these  evidently  were  not  joined  with  the  foot  by  appropriate  muscular  and 
tendinous  connections,  for  the  toe  hung  limply  down  from  the  side  of  the 
foot  like  a  bag  of  skin.  It  remained  attached  to  the  foot  until  the  animal 
was  fully  grown,  but  was  then  lost,  probably  having  been  accidentally 
pulled  off. 

Previous  to  the  birth  of  this  polydactylous  guinea-pig,  I  had  never  seen 
a  fourth  digit  on  the  hind  foot  of  a  guinea-pig,  nor  heard  of  its  occurrence 
either  among  wild  or  domesticated  Caviidse,  and  I  am  unable  to  find  any 
reference  to  such  a  character  in  the  literature  of  the  group.  But  I  have 
since  found  that  the  "  extra-toe  "  does  occur  not  infrequently  among  guinea- 
pigs  in  an  imperfectly  developed  condition,  and  I  have  twice  since  obtained 
animals  of  this  sort  from  breeders.  From  the  progeny  of  the  single  poly- 
dactylous individual  born  in  June,  1901,  a  well-established  race  of  four-toed 
guinea-pigs  has  now  been  formed.  An  account  of  how  this  was  done,  it 
is  hoped,  may  be  of  value  as  bearing  on  the  origin  of  breeds. 

17 


i8 


ORIGIN  OF  A  POLYDACTYLOUS  RACE  OF  GUINEA-PIGS. 


The  original  polydactylous  guinea-pig  (<$  23,  table  i,  p.  18),  was  born  to 
parents  of  almost  unknown  ancestry,  but  certainly  not  closely  related  to 
each  other.  The  mother,  a  spotted  animal  ($51)  produced  no  other  poly- 
dactylous offspring,  though  she  bore  in  all  thirty  young.  But  the  father 
((^4i.ia),  who  sired  in  all  one  hundred  and  forty-seven  young,  had  five 
other  polydactylous  offspring.  These  were  all,  except  one,*  borne  by  females 
descended  from  himself,  and  that  one  was  borne  by  his  half-sister  (J42.ia), 
so  that  it  seems  certain  that  the  polydactylous  character  came  in  every  case 
from  the  same  individual,  £  41. ia.  A  son  of  $  41.1* — viz,  $  243  (table  i) — 
whose  mother  was  half-sister  to  <$  41.1%  produced,  like  his  father,  a  certain 
number  (five)  of  polydactylous  offspring,  which  were  used  in  building  up 
the  polydactylous  race. 

TABLE  I.  — Ancestry  of  the  various  males  used  in  building  up  the  polydactylous  race. 
The  character  of  the  extra-toe  is  indicated  by  letters  following  the  numeral  which  designates  each  individual- 
These  letters  signify :  G,  good  ;  F,  fair;  P,  poor;  N,  normal,  i.  e.,  three-toed.     Read  downward. 

9*1  3f*.  Q4^ 

I    I 


d"/V/V 


gsi 
\ 

\              ~r 

3  41.1*                                                            Q42.I* 
1    1                                                                                1 

\                         \ 

\ 

pi.  A 

&/9O 
II 

I 

\ 

3-ff 
1 

l' 

Q30Q-NP: 
1 

461-TN.      QSI8-GG.     3l 
\ 

\ 

ll-GG     Pm-PH 
ii              ' 

'    "1  

3&28-GF:    fit 

f 

1"               1 
JO9-G6.    £8/0  -GO. 

$954  -GG. 

^1 

£>768-GG. 
1  !=f-J. 

dioc 

3-fG. 

~"i  r  "          "i  ' 

3635-FF.                                     PBI6-GG.                    3ll4O-GN. 
6ll65-GG.                        \ 

63046-GG. 


*  In  an  earlier  paper  (Castle,   105)  this  exception  was  inadvertently  overlooked, 
and  the  total  number  of  young  sired  by  c?4Ma  was  given  as  139  instead  of  147. 


ORIGIN  OF  A  POLYDACTYLOUS  RACE  OF  GUINEA-PIGS.  19 


2.    PROGENY   OF   THE   ORIGINAL   POLYDACTYLOUS   INDIVIDUAL. 

The  polydactylous  male  ((^23),  in  a  total  of  seventy-seven  young, 
produced  fifteen  polydactylous  ones.  The  proportion  of  polydactylous 
individuals  varied  much  among  the  offspring  by  different  mothers.  (See 
table  2.)  Unrelated  mothers,  from  families  in  which  polydactylism  had 
not  been  observed,  gave  only  two  polydactylous  young  to  thirty  normal 
ones,  or  6.25  per  cent,  polydactylous.  Related  normal  mothers — that  is, 
mothers  descended  from  <$  41.  ia — gave  nine  polydactylous  to  twenty-seven 
normal,  or  25  per  cent,  polydactylous,  while  polydactylous  mothers  gave 
four  polydactylous  to  five  normal  young,  or  44  per  cent,  polydactylous  young. 

Many  of  the  young  of  ^23  had  the  extra  digit  present  on  both  the 
right  and  the  left  hind  feet,  and  in  several  of  these  the  digits  were  better 
developed  than  in  the  father,  evidently  with  all  the  appropriate  muscles 
necessary  for  functional  toes.  One  of  the  best  of  these  young  was  (£193 
(table  i).  His  mother  was  a  normal  individual  descended  from  <$  41.1*,  but 
gave  a  larger  proportion  of  polydactylous  young  than  any  other  mother  had 
done  up  to  that  time.  By  <$  23  she  had  five  polydactylous  and  six  normal 
young. 

To  express  the  degree  of  development  of  the  extra  digit  a  series  of 
three  grades  was  now  established,  good,  fair  and  poor,  which  will  be  abbre- 
viated to  G,  F  and  P  respectively.  Good  means  a  fully  developed  and  func- 
tional fourth  toe;  fair  means  a  fourth  toe  rather  smaller  than  the  others, 
often  turned  upward  a  little  in  walking,  as  if  its  muscular  equipment  were 
imperfect ;  poor  means  a  loosely  hanging  toe,  either  with  or  without  a  nail ; 
sometimes  the  toe  described  as  poor  is  represented  by  only  a  soft  fleshy  bag 
of  skin  attached  to  the  side  of  the  foot,  without  either  nail  or  hair,  destined 
to  shrivel  up  and  drop  off  within  a  few  days  after  birth.  In  distinction  from 
these  three  classes,  the  term  normal  (N)  will  be  used  to  describe  a  three- 
toed  foot.  In  describing  the  condition  of  the  toes  of  an  individual,  the  left 
foot  will  always  be  named  first;  thus  GP  will  mean  an  individual  having  a 
good  fourth  toe  on  the  left  foot,  a  poor  one  on  the  right  foot. 

3.    PROGENY   OF   THE   SECOND   POLYDACTYLOUS   GENERATION. 

Male  193,  as  regards  the  extra-toe,  was  classed  as  FF,  but  he  pro- 
duced about  fifteen  young  with  well-developed  extra-toes,  which  placed 
them  in  class  G.  About  one-fourth  of  all  his  polydactylous  young  were  of 
this  sort,  the  polydactylous  including  more  than  half  his  young  (forty- 
eight  out  of  eighty-six). 


20  ORIGIN  OF  A  POLYDACTYLOUS  RACE  OF  GUINEA-PIGS. 


METHOD  OF  GRADING  THE  PROGENY. 

Of  course  the  female  mates  of  $  193  were  in  many  cases  superior  in 
toe  development  to  the  mates  of  his  father,  <£  23,  though  in  many  cases  they 
were  identical.  Accordingly  it  is  necessary,  in  estimating  the  respective 
potency  of  the  two  animals,  to  separate  the  mothers  into  groups  of  similar 
toe  development,  or  of  similar  pedigree  when  no  extra-toes  were  present. 
Consequently,  five  groups  of  mothers  have  been  made  (see  tables  2-14), 
viz,  G,  F,  P,  N  and  N'.  Group  G  includes  only  mothers  having  well-devel- 
oped extra-toes  on  both  feet  (GG)  ;  F  includes  mothers  having  fairly  well- 
developed  toes,  or  with  one  good  toe  only  (FF,  FG,  or  GF*)  ;  P  includes 
mothers  with  at  least  one  toe  poorly  developed  (P)  ;  the  other  toe  may  be  fair 
or  poor,  or  the  foot  may  be  normal.  N  includes  normal  (NN)  mothers 
descended  from  J*  41.1*  or  nearly  related  to  him;  N'  includes  normal  mothers 
not  descended  from  <^4i.ia,  but  belonging  to  families  in  which,  when 
inbred,  polydactylism  does  not  occur. 

When  the  mothers  are  grouped  in  this  way,  we  find,  first,  that  the  pro- 
portion of  polydactylous  young  produced  by  a  male  decreases  in  the  suc- 
cessive classes  from  G  to  N'  ;  and  secondly,  that  the  degree  of  development 
of  the  toes  produced  on  those  polydactylous  young  diminishes  in  the  same 
order. 

It  would  manifestly  be  unfair  in  estimating  the  potency  of  transmission 
in  a  given  case  to  omit  either  of  these  considerations  —  the  proportion  of 
polydactylous  young,  or  the  degree  of  development  of  their  extra-toes.  So 
an  attempt  has  been  made  to  combine  the  two  into  a  numerical  grade  for 
the  young  by  each  group  of  mothers.  This  grade  is  given  in  the  last 
column  of  tables  2  to  14.  In  making  up  the  grade  each  G  toe  counts 
100,  each  F  toe  80,  and  each  P  toe  50,  while  N  counts  o.  The  total  thus 
obtained  for  a  group  of  young  is  divided  by  twice  the  total  number  of 
young  in  that  group,  that  is,  by  the  whole  number  of  feet  which  might  bear 
the  extra-toe.  Measured  by  this  standard,  a  group  of  young,  all  of  which 
had  the  extra-toe  well  developed  on  both  hind  feet,  would  be  graded  100; 
a  group  of  young  with  no  extra-toes  would  be  graded  o,  while  mixed  groups 
would  come  in  between  o  and  100.  A  group  of  young  averaging  P  would 
be  graded  50,  and  a  group  averaging  F  would  be  graded  80. 

Comparing  the  young  of  <$  193  (table  3)  with  those  of  his  father,  ^23 
(table  2),  we  see  a  marked  increase  in  the  potency  of  transmission  of  the 
extra-toe  within  the  same  group  of  mothers.  The  grades  of  the  young 
produced  by  the  last  four  groups  of  mothers  (F  to  N')  in  the  case  of  $  23 
are  29,  19,  17,  and  1.5,  respectively,  while  in  the  case  of  $  193  they  are 
58,  57.5,  22  and  18.5. 


ORIGIN  OF  A  POLYDACTYLOUS  RACE  OF  GUINEA-PIGS.          2  I 


4.     PROGENY    OF    THE    THIRD    POLYDACTYLOUS    GENERATION. 

Continuing  to  trace  the  history  of  the  polydactylous  race  in  the  male 
line,  we  may  notice  that  the  sires  of  the  next  generation  of  young  consisted 
of  four  sons  of  £  193.  Two  of  these  were  own  brothers,  viz,  £  628  and 
<$  809  (see  table  i).  The  other  two  were  half-brothers  to  these  two  and  to 
each  other.  They  were  ^635  and  c?7ii.  The  young  of  these  four  males 
are  classified  as  regards  the  extra-toe  character  in  tables  4  to  7  (see  pages 
25  and  26).  An  examination  of  these  tables  shows  for  <$  809  an  increase  of 
potency  over  that  of  his  father,  <$  193;  $  711  shows  a  potency  very  similar 
to  that  of  his  father,  but  the  other  two  males,  £  628  and  $  635,  are  clearly 
inferior  to  their  father  in  potency,  their  average  grades  being  about  34  and 
38  respectively,  while  that  of  their  father  was  46. 


5.    PROGENY    OF    THE    FOURTH    POLYDACTYLOUS    GENERATION. 

The  sires  of  the  next  generation  consisted  of  six  males,  four  of  which 
were  sons  of  the  best  male  (809)  of  the  previous  generation,  while  one  was 
a  son  of  ,^628,  and  one  a  son  of  c?7H.  Considering  first  the  four  sons 
of  <$  809  (table  7),  we  notice  that  three  of  them,  <$  954  (table  8),  $  1140 
(table  10)  and  $  1264  (table  13),  are  clearly  inferior  to  their  father  in 
potency.  The  fourth  male,  <$  1263  (table  12),  makes  a  somewhat  better 
showing  than  his  father,  though  two  of  the  possible  groups  of  mothers  (F 
and  N)  are  wholly  unrepresented  among  his  mates  and  their  values  can 
only  be  roughly  estimated  by  interpolating  values,  while  two  other  groups 
are  very  inadequately  represented.  Yet  all  the  data  available  agree  in 
showing  high  potency  on  the  part  of  this  male.  Out  of  a  total  of  eighty-three 
young  which  he  has  sired,  only  one  has  been  three-toed. 

Male  1003  (table  9)  has  a  record  similar  to  that  of  his  father,  $  628 
(table  4),  but  on  the  whole  better.  It  is  noteworthy  that  neither  of  these 
animals  gave  polydactylous  offspring  when  mated  to  unrelated  normal 
females,  though  by  polydactylous  mothers  they  had  a  good  proportion  of 
polydactylous  young. 

Male  1165  (table  u),  also,  has  a  record  like  that  of  his  father,  <$  711 
(table  6).  By  unrelated  normal  (Nf)  females  he  produced  offspring  grad- 
ing 10  as  regards  the  extra-toe  character,  his  father's  offspring  by  the  same 
group  of  mothers  grading  8.  By  matings  with  polydactylous  mothers,  both 
father  and  son  have  produced  offspring  grading  below  those  of  $  809  and 
of  <$  1263. 


22  ORIGIN  OF  A  POLYDACTYLOUS  RACE  OF  GUINEA-PIGS. 


6.  PROGENY  OF  THE  FIFTH  POLYDACTYLOUS  GENERATION. 
Only  one  male,  ^3046  (tables  I  and  15),  in  this  generation,  has  been 
extensively  tested,  and  he  has  been  used  almost  exclusively  in  matings  with 
the  best  four-toed  stock.  His  young  in  that  sort  of  mating  grade  very 
high,  viz  97,  the  standard  of  perfection  being  100.  He  was  mated  to  a 
female  of  class  N'  a  single  time,  and  produced  three  normal  offspring  and 
one  polydactylous ;  these  three  were  the  only  normal  young  he  ever  got  in 
a  total  of  ninety- two  young.  But  this  same  mother  bore  to  J*  1263  a  litter 
of  four  young,  all  polydactylous.  Facts  like  this  indicate  characteristic 
potencies  on  the  part  of  gametes  furnished  by  certain  individuals,  these 
potencies  perhaps  being  handed  on  from  generation  to  generation,  as  from 
$  628  to  his  son,  $  1003. 

7.    INDIVIDUAL   POTENCY  VERSUS  ANCESTRY. 

The  factor  of  gametic  potency  is  evidently  much  greater  than  that  of 
ancestry.  For  if  we  arrange  the  various  sires  in  the  order  of  the  respective 
amounts  of  polydactylous  ancestry  which  they  possess  (table  15),  we  see 
at  once  that  this  is  not  the  order  of  their  potencies,  for  those  having  the 
same  amount  of  polydactylous  ancestry  often  differ  much  in  the  potency  with 
which  they  transmit  the  polydactyl  character. 

8.    EXTRA-TOE  OF  LEFT  SIDE  BEST  DEVELOPED. 

The  extra-toe,  in  the  case  of  <$  23,  was  found  on  the  left  side  of  the 
body  only.  Among  his  descendants,  also,  the  extra-toe,  if  present  on  one 
side  of  the  body  only,  is  more  apt  to  be  found  on  the  left  side.  When  the 
extra-toe  is  found  on  both  sides  of  the  body,  but  unequally  developed,  it  is 
oftener  the  left  side  which  has  the  better  developed  toe.  The  difference  is 
not  great,  but  is  quite  constant.  Thus  there  have  been  recorded  the  follow- 
ing numbers  of  polydactylous  feet :  Left,  630 ;  right,  589.  These  totals  are 
made  up  from  various  partial  sums  given  by  different  generations  or  families 
as  follows: 

Total. 

Left     61    66    51    41    18    98    112    21    51    34    24    53       630 
Right  56    65    50    39    15    86    in    20    50    32    20    45        589 

In  every  case  the  left  toes  slightly  outnumber  the  right  ones. 

The  extra-toes,  as  regards  both  degree  of  development  and  position  on 
the  body,  are  distributed  as  shown  in  table  16. 

The  extra-toe,  it  will  be  observed,  occurs  oftenest  on  the  left  side  of 
the  body,  particularly  in  its  higher  grades  of  development  (G  and  F). 


ORIGIN  OF  A  POLYDACTYLOUS  RACE  OF  GUINEA-PIGS.          23 

The  attempt  has  twice  been  made  to  increase  by  selection  the  asymmetry 
of  the  two  sides  of  the  body  with  reference  to  the  extra-toe,  but  without 
success.  The  slightly  superior  development  of  the  extra-toe  on  the  left 
side  of  the  body  apparently  remains  unaffected.  The  cause  of  the  asymmetry 
is  unknown.  The  case  doubtless  belongs  in  the  same  category  as  the 
unequally  developed  right  and  left  sex-glands  of  certain  birds  and  mammals. 

9.    RESULT   OF   MATING   NORMAL   WITH    POLYDACTYLOUS   INDIVIDUALS. 

Matings  between  normal  females  and  polydactylous  males  have  repeat- 
edly been  made,  as  will  appear  from  tables  2  to  14.  Crosses  reciprocal  to 
these  have  yielded  the  results  indicated  in  table  17.  The  results,  it  will  be 
seen,  are  not  uniform.  The  offspring  have,  in  some  cases,  a  greatly  weak- 
ened condition  of  the  extra-toe,  in  other  cases  no  extra-toe  at  all ;  in  still  other 
cases,  the  extra-toe  may  be  present  in  a  fairly  well-developed  condition. 
The  inheritance  is  evidently  neither  sharply  alternative  («.  e.,  Mendelian) 
nor  completely  blending.  The  result  of  a  cross  involving  the  extra-toe 
character  is  influenced  by  the  individual  potency  of  the  respective  parents. 
Fewer  polydactylous  young  are  produced  if  the  normal  parent  comes  of  a 
stock  in  which  the  polydactylous  character  does  not  occur. 

10.  INHERITANCE  NEITHER  ALTERNATIVE  NOR  BLENDING. 

It  is  very  evident  that  in  the  inheritance  of  the  extra-toe  we  are  not 
dealing  with  a  case  of  simple  Mendelian  dominance.  An  occasional  case, 
like  the  matings  of  ^628  with  normal  females  (see  table  4),  would  indicate 
that  the  extra-toe  is  a  recessive  character,  but  most  polydactylous  parents, 
in  matings  with  normal  individuals,  give  a  mixture  of  normal  with  poly- 
dactylous offspring.  Further,  in  these  mixed  lots  of  offspring,  the  polydac- 
tylous and  normal  individuals  are  rarely  equal  to  each  other  in  number,  as  we 
should  expect  if  one  parent  were  a  Mendelian  heterozygote,  the  other  pure. 

On  the  other  hand,  when  two  of  the  offspring  produced  by  a  cross 
between  polydactylous  and  normal  parents  are  mated  together,  we  do  get 
some  evidence  of  Mendelian  segregation.  The  offspring  are  highly  variable 
as  regards  the  character,  extra-toe.  Some  are  normal,  some  have  poorly 
developed  toes,  and  some  have  very  well  developed  toes.  The  experiments 
are  still  incomplete  as  regards  this  matter,  but  so  far  do  not  indicate  the  for- 
mation of  sharply  separated  Mendelian  classes. 

On  the  whole,  it  seems  probable  that  the  extra-toe  is  inherited  in  a 
manner  intermediate  between  blending  and  alternative  inheritance.  The 
gametes  only  partially  blend  in  the  zygote,  producing  a  variable  result,  most 


24          ORIGIN  OF  A  POLYDACTYLOUS  RACE  OF  GUINEA-PIGS. 

often  an  intermediate  condition.  The  gametes  formed  by  the  cross-breds 
are  not  homogeneous,  as  would  be  the  case  if  complete  blending  occurred 
in  the  zygote,  but  are  highly  variable  as  regards  the  extra-toe.  If  the  inher- 
itance were  sharply  alternative,  we  should  expect  to  get,  not  a  series  of 
graduated  forms,  but  two  or  at  most  three  sharply  distinct  groups,  but  this 
is  not  the  observed  result.  If,  on  the  other  hand,  inheritance  were  fully 
blending,  all  the  offspring  of  two  pure  parents,  or  of  two  cross-bred  parents, 
should  be  alike,  but  this  is  not  the  observed  result.  We  are  forced  to 
conclude,  therefore,  that  there  occurs  a  partial  blending  of  gametes  in  the 
zygote,  and  a  partial  segregation  as  the  zygote  gives  off  gametes. 

Not  improbably  more  characters  fall  in  this  category  than  in  any  other. 
Sharp  alternative  inheritance  is  comparatively  rare,  so  is  fully  blending 
inheritance ;  most  characters  appear  from  generation  to  generation  in  a  more 
or  less  well  developed  condition,  not  always  strictly  intermediate  between 
the  conditions  found  in  the  respective  parents,  nor  always  corresponding 
closely  either  with  the  condition  found  in  one  parent  or  with  that  found  in 
the  other.  In  dealing  with  such  characters,  selection  must  be  the  breeder's 
method  of  working.  If  he  wishes  either  to  eliminate  or  to  "  fix  "  a  par- 
tially blending  character  he  must  make  an  appropriate  choice  of  parents, 
not  once  nor  twice,  but  many  times  over  until  the  undesired  condition  ceases 
wholly  to  reappear. 

It  would  be  interesting  to  know  in  what  condition  characters  like  the 
extra-toe  exist  in  the  germ.  It  can  not  be  in  a  state  of  simple  recessiveness, 
for  in  that  case  the  character  should  reappear  in  a  Mendelian  proportion 
of  the  offspring  formed,  but  this,  as  we  have  seen,  is  not  the  case.  More 
probably  the  character  is  present,  active  or  inactive,  in  every  gamete,  but 
the  conditions  under  which  it  may  become  active  are  too  complex  for  present 
analysis.  On  the  other  hand,  it  is  possible  that  nothing  in  the  germ  of  a 
normal  guinea-pig  stands  for  the  character,  extra-toe,  and  that  when  this 
character  is  formed,  it  is  formed  de  novo.  But  if  so,  we  must  account 
for  the  appearance  of  a  new  digit  in  the  precise  position  of  a  lost  one, 
and  with  all  the  appropriate  nervous  and  muscular  connections.  This 
it  seems  quite  as  hard  to  do  as  to  suppose  an  antecedent  state  of  latency  or 
inactivity  of  the  character  throughout  certain  generations  of  ancestors. 
Moreover,  we  have  strong  reasons  for  believing  that,  in  color  inheritance, 
specific  pigments  and  specific  color  patterns  may  be  transmitted  unseen  in 
a  latent  condition,  often  through  long  series  of  generations.  If  color  char- 
acters are  subject  to  transmission  in  a  latent  condition,  it  seems  reasonable 
to  suppose  that  other  characters  also  may  be  transmitted  in  the  same  way. 


ORIGIN  OF  A  POLYDACTYLOUS  RACE  OF  GUINEA-PIGS.          25 
TABLE  2. — Character  of  the  extra-toe  in  young  of  $  23  (PN),  of  polydactylous  generation  I. 


Character  of 
mother. 

G 
L     R 

F 
L     R 

p 
L     R 

N 
L     R 

Total  polydac- 
tylous indi- 
viduals. 

Total  normal 
(AW)  indi- 
viduals. 

Per  cent, 
polydac- 
tylous. 

Grade. 

G 

F 

2—1 

—  I 

2 

3 

40 

29 

P 

2—1 

—I 

2 

2 

5° 

19 

N 

4—5 

2—2 

3—2 

9 

27 

25 

n 

N' 

2— 

—  2 

2 

3° 

6 

1.5 

6-6 

6-4 

3—5 

15 

62 

19-5 

22(?) 

TABLE  3.* — Character  of  the  extra-toe  in  young  of  $  193  (FF),  generation  II. 


Character  of 

G 

F 

/> 

N 

Total  polydac- 

Total  normal 
(AW)  indi- 

Per cent. 

Grade. 

L     R 

L     R 

L     R 

L     R 

viduals. 

viduals. 

tylous. 

G 
F 
P 

AT 

Ei 

I— 

5—  4 
10—  7 

2—  4 

i—3 

2 

8 

19 
16 

2 

5 
26 

*£ 
3 

CI] 

57.5 

99 

N' 

i  —  i 

I  —  I 

3 

4 

43 

18.5 

*5—  13 

20  —  14 

7—13 

6—8 

48 

38 

56 

46 

TABLE  4. — Character  of  the  extra-toe  in  young  of  $  628  (  GF),  generation  III. 


Character  of 
mother. 

G 

F 

P 

N 

Total  polydac- 
tylous indi- 
viduals. 

Total  normal 
(AW)  indi- 
viduals. 

Per  cent, 
polydac- 
tylous. 

Grade. 

L     R 

L     R 

L     R 

L     R 

G 

I  —  I 

I  —  I 

2 

[100] 

[90] 

F 

I  | 

j 

2 

ri7i 

P 

7-5 

i  —  3 

4—3 

I  —  2 

13 

2 

87 

62 

N 

4 

O 

0 

N' 

8 

o 

0 

8-6 

2—4 

5—4 

I  —  2 

26 

16 

62 

34 

TABLE  5. — Character  of  the  extra-toe  in  young  of  $  635  (FF),  generation  III. 


Character  of 
mother. 

G 

F 

P 

L     R 

Total  polydac- 
tylous indi- 
viduals. 

Total  normal 
(AW)  indi- 
viduals. 

Per  cent, 
polydac- 
tylous. 

Grade. 

L     R 

L        R 

L        R 

G 

2  —    I 

—   I 

2 

I 

[67] 

[251 

F 

I  —  I 

2  —  2 

3 

[100] 

RKl 

P 

4—  4 

4—  4 

—  2 

ii 

7 

78 

N 

3—2 

8—  8 

ii—  7 

I—  6 

23 

32 

42 

24 

N' 

3—  3 

7—  3 

—  4 

10 

24 

29 

14 

7—4 

17—17 

24—15 

1—13 

49 

64 

43 

38 

*In  the  last  two  columns  of  tables  3  to  13,  per  cent,  or  grades  of  the  young,  when  based  on  a 
smaller  number  of  individuals  than  four,  are  placed  within  brackets. 


26  ORIGIN  OF  A  POLYDACTYLOUS  RACE  OF  GUINEA-PIGS. 

TABLE  6. — Character  of  the  extra-toe  in  young  of  $  711  ( GG),  generation  III. 


Character  of 
mother. 

G 

F 

P 

N 

Total  polydac- 
tylous  indi- 
viduals. 

Total  normal 
(JWV)  indi- 
viduals. 

Per  cent, 
polydac- 
tylous. 

Grade. 

L       R 

L    R 

L    R 

L    R 

G 

F 
P 

N 
N' 

7-  7 

I  —  I 

I—  4 

II—IS 

I—  I 
2—2 
2—1 

3—i 
I—  I 

3—2 

3—2 

4—3 

I—  I 
—  I 

8 

7 

\ 

e 

2 
27 

100 

78 

57 
So 
12.5 

97.5 
60 
42 
33 

~48~ 

9-6 

II—  9 

I  —  2 

32 

40 

44 

TABLE  7. — Character  of  the  extra-toe  in  young  of  $  809  ( GG},  generation  III. 


Character  of 
mother. 

G 

F 

p 

N 

Total  polydac- 
tylous  indi- 
viduals. 

Total  normal 
(AW)  indi- 
viduals. 

Per  cent, 
polydac- 
tylous. 

Grade. 

L        R 

L    R 

L    R 

i—3 

2—1 

5—4 

L    R 

G 
F 
P 

N 

N' 

28—24 
4—  4 
4—  3 
i  — 
i  — 

4—7 
3—3 

1—2 

—2 
1—2 

34 
4 

9 

i 
8 

I 

6 

97 
80 

100 

[5°] 
57 

90 
80 
74 

[y] 

38—31 

8-13 

8—8 

8—8 

56 

9 

86 

63 

TABLE  8. — Character  of  the  extra-toe  in  young  of  $  954  (  GG),  generation  IV. 


Character  of 
mother. 

G 

F 

P 

N 

Total  polydac- 
tylous  indi- 
viduals. 

Total  normal 
(AW)  indi- 
viduals. 

Per  cent, 
polydac- 
tylous. 

Grade. 

L      R 

L      R 

L      R 

L     R 

G 

F 
P 

N 
Nf 

9—  9 

3—  2 
7—5 
i—  3 

3—  3 
3—  4 
7—  9 

2  — 

6-5 
i  —  i 

10  —  10 

4-  5 
i  — 

1—2 
2—2 
—  I 

19 

,1 

8 
i 

2 

3 
i 
i 

£s 

5 

[50] 

67 
73 

60 
56 

[12.5] 

20  —  19 

I5—I6 

22  —  21 

4-5 

61 

8 

88 

54 

TABLE  9. — Character  of  the  extra-toe  in  young  of  $  1003  (FG),  generation  IV. 


Character  of 
mother. 

G 

F 

P 

N 

Total  polydac- 
tylous  indi- 
viduals. 

Total  normal 
(AW)  indi- 
viduals. 

Per  cent, 
polydac- 
tylous. 

Grade. 

L     R 

L     R 

L     R 

L     R 

G 

6—6 

6 

100 

100 

F 

P 

N 

3—3 

2-1 

—  2 

I  — 

6 

3 

67 

52 

N' 

20 

O 

0 

9—9 

2  —  I 

—2 

I— 

12 

23 

34 

51 

ORIGIN  OF  A  POLYDACTYLOUS  RACE  OF  GUINEA-PIGS.          27 
TABLE  10.— Character  of  the  extra-toe  in  young  of  $  1 140  (  GN),  generation  IV. 


Character  of 
mother. 

G 

F 

P 

N 

Total  polydac- 
tylous  indi- 
viduals. 

Total  normal 
(AW)  indi- 
viduals. 

Per  cent, 
polydac- 
tylous. 

Grade. 

L     R 

L     R 

L     R 

L     R 

G 

F 

3—2 

2—3 

4—1 

—3 

9 

2 

82 

48 

P 

4—2 

3—3 

4—4 

i—3 

12 

3 

80 

4» 

N 

3—2 

2  —  2 

—  i 

5 

i 

83 

72.5 

N' 

1  10  —  6 

7-8 

8—6 

i—6 

26 

6 

8l 

56.5 

TABLE  il.— Character  of  the  extra-toe  in  young  of  $  1165  (GG),  generation  IV. 


Character  of 
mother. 

G 

P 

P 

N 

Total  polydac- 
tylous  indi- 
viduals. 

Total  normal 
(AW)  indi- 
viduals. 

Per  cent, 
polydac- 
tylous. 

Grade. 

L       R 

L        R 

L     R 

L       R 

G 

32-30 

5-  7 

2  —  2 

39 

2 

95 

QA 

F 

4—  4 

5—  5 

I  —  I 

IO 

IOO 

85 

P 

2  —    I 

I  —  2 

3 

2 

60 

45 

N 

N' 

i—3 

2— 

3 

7 

30 

10 

38-35 

IO  —  12 

5-8 

2  — 

55 

ii 

83 

50 

TABLE  12.— Character  of  the  extra- toe  in  young  of  $  1263  (  GG),  generation  IV. 


Character  of 
mother. 

G 
L      R 

F 

P 

N 

Total  polydac- 
tylous  indi- 
viduals. 

Total  normal 
(AW)  indi- 
viduals. 

Per  cent, 
polydac- 
tylous. 

Grade. 

L      R 

L     R 

L     R 

G 

66—61 

6—  6 

5—9 

I 

77 

IOO 

93 

F 

P 

N 

2  —  2 

2 

I 

[67] 

[67] 

N' 

I— 

3—  4 

4 

IOO 

82.5 

69-63 

9  —  10 

5—9 

-I 

83 

I 

99 

81 

TABLE  13. — Character  of  the  extra-toe  in  young  of  $  1264  (GG),  generation  IV. 


Character  of 
mother. 

G 

F 

p 

N 

Total  polydac- 
tylous  indi- 
vidual.. 

Total  normal 
(AW)  indi- 
viduals. 

Per  cent, 
polydac- 
tylous. 

r  97',5 
1 

Grade. 

L      R 

L      R 

L      R 

L     R 

G 
F 
P 

N 

N' 

21  —  22 
I  —    I 

6-5 

12  —  9 

3—  2 

2—  4 

—   I 

3—  4 

2  —  2 

I  —  I 
—  I 

36 

2 
12 

2 

I 

2 
4 
3 

85 

C|i.5] 

17 

[0] 

28—28 

16—  ii 

7—  ii 

1—2 

52 

IO 

84 

50 

28  ORIGIN  OF  A  POLYDACTYLOUS  RACE  OF  GUINEA-PIGS. 

TABLE  14. — Character  of  the  young  of  $  3046  (GG),  generation  V. 


Character  of 
mother. 

G 

f 

P 

N 

Total  polydac- 
tylous  indi- 
viduals. 

Total  normal 
(AW)  indi- 
viduals. 

Per  cent, 
polydac- 
tylous. 

Grade. 

L      R 

L     R 

L     R 
I  —  2 

L    R 

G 

N' 

79—77 

8—8 

—  I 

88 

O 

3 

IOO 
25 

97 

8 

79—77 

8—8 

2  —  2 

—  I 

89 

3 

97 

TABLE  15. — Sires  gfouped  by  generations  of  polydactylous  ancestry. 

[The  numerals  in  parenthesis  indicate  rank  in  potency  of  transmission  of  the  polydactylous  character.     Descent  is 
shown  in  the  male  line  only.] 


Poiydactylous 
generations 
in  ancestry. 

0 

X 

• 

»# 

2 

2/2 

3 

, 

628(4) 

iocn(3) 

63<5(4) 

21(5) 

10^(3)  J 

7ii(3) 

1165(8) 

3046(1) 

r 

Q<>4(3) 

8oo(2)  \ 

1140(8) 

1263(1) 
1264(8) 

Generation  (in 
male  line) 

L 

II. 

I 

[I. 

IV 

V. 

TABLE    16. — Frequency  of  occurrence  of  the  extra-toe  in  its  several 
degrees  of  development  on  the  two  sides  of  the  body. 


Left  side. 

Right  side. 

Per  cent.  left. 

G 
F 
P 

335 
148 

»47 

3IO 

133 
146 

51-9 
52-6 
50.2 

630 

589 

51.6 

TABLE  17. — Character  of  the  young  produced  by  a  mating  between  a  normal  (W)  male  and 
females  either  polydactylous  or  of  polydactylous  ancestry. 


Father. 

Character  of 
mother. 

F 
L     R 

P 

N 

Total  polydac- 
tylous indi- 
viduals. 

Total  normal 
(AW)  indi- 

Per  cent, 
polydac- 
tylous. 

Grade. 

L     R 

L     R 

$     482 

P 

I  — 

I  — 

-2 

2 

O 

[IOO] 

[32.5] 

$     981 

F 
P 

2  —  I 

2-3 

I  —  2 

3 
3 

2 

O 

60 
[IOO] 

15 

[25] 

$  2054 

P 

N 

—  I 

I  — 

o 

4 

5 

0 

17 

0 

$  2060 

G 

2  —  I 

4-5 

6 

10 

37-5 

22 

23609 

G 

2  —  I 

—  I 

2 

6 

25 

9 

ORIGIN  OF  A  POLYDACTYLOUS  RACE  OF  GUINEA-PIGS.          29 

POSTSCRIPT. 

A  critical  examination  of  the  results  obtained  by  Bateson,  Punnett  and 
Hurst  (see  Bateson,  Saunders,  Punnett  and  Hurst,  105)  in  poultry  indicates 
that  there  too  the  inheritance  of  extra-toe  is  not  strictly  Mendelian,  but  cor- 
responds with  what  I  have  found  to  be  the  condition  in  the  most  potent  poly- 
dactylous  sires.  In  poultry  the  extra-toe  has  been  for  a  long  time  an  estab- 
lished character  of  certain  breeds.  During  all  that  time  selection  has  un- 
doubtedly been  exercised  in  its  favor,  so  that  it  is  not  surprising  to  find  the 
character  more  strongly  dominant  than  in  my  four-toed  race  of  guinea-pigs. 
Nevertheless  both  Bateson  and  Hurst  record  cases  in  which  polydactylous 
chicks  are  produced  by  normal  parents  of  polydactylous  ancestry. 

Similar  observations  have  repeatedly  been  made  concerning  the  inher- 
itance of  polydactylism  in  man.  See  Ballowitz  (  -.04)  and  Davenport  (  104). 
Polydactylism  usually  makes  its  (recorded)  appearance  in  some  note- worthy 
form,  is  transmitted  more  or  less  strongly  through  two  to  five  generations 
and  then  disappears,  doubtless  so  weakened  by  repeated  out-crosses  that  its 
manifestations,  if  any  occur,  are  no  longer  observed. 

Apparently  it  is  only  when  selection  is  exercised  for  the  polydactyl 
character  and  like  individuals  are  mated  to  each  other  that  a  polydactylous 
race  can  be  established.  In  its  origin,  polydactylism  is  a  discontinuous  varia- 
tion or  mutation,  but  without  the  aid  of  selection  it  would  probably  never 
become  a  racial  character.  Is  not  the  same  thing  true  of  a  great  many  of 
the  characters  which  serve  to  distinguish  the  various  races  of  domesticated 
animals  and  plants  ? 

11.    BIBLIOGRAPHY. 

BALLOWITZ,  E. 

104.    Ueber  hyperdactyle  Familien  und  die  Vererbung  der  Vielfingerigkeit  des 
Menschen.    Archiv.    f.   Rassen-und-Gesellschafts-Biol.    Bd.    i,   pp.   347- 
365,  ii  Fig. 
BATESON,  W.,  SAUNDERS,  E.  R.,  PUNNETT,  R.  C,  and  HURST,  C.  C. 

:os.    Experimental  Studies  in  the  Physiology  of  Heredity.    Report  II.  to  the 

Evolution  Committee  of  the  Royal  Society.     154  pp. 
CASTLE,  W.  E. 

.•05.    The  Mutation  Theory  of  Organic  Evolution,  from  the  Standpoint  of  Animal 

Breeding.     Science,  n.  s.,  vol.  21,  no.  536,  pp.  521-525. 
DAVENPORT,  C.  B. 

:04.     Wonder  horses  and  Mendelism.     Science,  n.  s.,  vol.  19,  no.  473,  pp.  151-153. 


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